The present invention relates to a resist application method and device for applying a resist to a substrate after the surface of the substrate has been subjected to hydrophobic processing with hexamethyldisilazane.
Conventionally in fabricating semiconductor devices, when a resist is applied to a substrate, such as a wafer or others, generally the surface of the substrate is made hydrophobic with hexamehtyldisilazane (HMDS) as pre-processing. HMDS is a good silylation agent, and easily silylates hydroxyl groups on the surface of the silicon substrate, etc. to make the substrate surface hydrophobic.
The hydrophobic processing with HMDS enhances adhesion between the resist film and the substrate surface, whereby in the following patterning, the occurrence of unsatisfactory pattern transfer, etc. can be suppressed.
The hydrophobic processing of a wafer surface with HMDS is made as follows.
First, HMDS, which is liquid at the room temperature, is bubbled with nitrogen gas while being heated. The nitrogen gas containing the HMDS produced by the bubbling is injected to a substrate on a hot plate whose temperature is controlled within a range of 30–100° C. in a tightly closed processing chamber.
Then, usually the substrate is cooled at the room temperature, and a certain amount of resist is dropped onto the rotating substrate in an environment whose temperature and humidity are controlled, whereby the resist is applied to the substrate. The resist applied to the substrate is dried and solidified by heat processing, and a resist film is formed. The resist film thus formed on the substrate is subjected to an exposure step to be patterned into a required shape, as of a wiring pattern or others.
In such resist applying step, for better adhesion between the resist and the substrate, various methods have been so far proposed.
For example, Japanese Published Patent Application No. Hei 04-99310 (1992) (pp. 2–3, FIGS. 1 and 2) discloses the method that prior to the HMDS processing, heated nitrogen gas is injected to a substrate to thereby remove water from the substrate surface.
Japanese Published Patent Application No. Hei 05-315233 (1993) (Paragraphs 0021–0022, FIG. 2) and Japanese Published Patent Application No. Hei 06-302507 (1994) (Paragraphs 0014–0015, FIG. 1) disclose the method that prior to the HMDS processing, water on the surface of a substrate is removed by reduced pressure processing.
Japanese Examined Patent Application Publication No. Sho 62-35264 (1987) (pp. 2–3, FIGS. 1–3) discloses the method that the processing from the HMDS processing to the application of the resist is performed in a nitrogen atmosphere.
Japanese Published Patent Application No. Hei 10-256139 (1998) (Paragraphs 0026–0033, FIG. 1) discloses the method that dry air is caused to flow in a coater cup where a resist is applied, for the purpose of removing humidity around the coater cup and recycling the resist.
Japanese Published Patent Application No. Hei 05-234866 (1993) discloses the method that a plasma processing unit and an HMDS processing unit are disposed in one and the same chamber to thereby remove water on substrate surfaces by plasma processing.
The internal unit of the resist application device, where the above-described resist application is performed is fed with an atmosphere in a clean room through a HEPA (High Efficiency Particulate Air) filter. Recently, in applying a chemically amplified resist used for mass production, an atmosphere in a clean room is fed into the internal unit through a chemical filter so as to remove basic substances, such as ammonia, etc., which inactivate the resist.
However, in the conventional resist application device, the humidity of an atmosphere in a clean room, which is to be fed into the internal unit, has not been especially controlled.
Accordingly, HMDS used for the hydrophobic processing before the resist application reacts with water contained in the fed atmosphere of the clean room to be decomposed into siloxane-group substances, such as trimethylsilanol. Resultantly, it is often that the adhesion between the resist and substances is lowered.
For the prevention of such reaction of HMDS with water in the atmosphere, as described above in connection with the prior art, a resist application device which controls the water content of the atmosphere in the HMDS processing unit is also so far known. However, the water contents of the atmosphere before and after the HMDS processing have not been controlled. For example, in cooling a substrate after the baking prior to the HMDS processing, in transferring the substrate or in cooling the substrate after the HMDS processing, the water contents of the atmosphere have not been especially controlled. Accordingly, re-adsorption of water to the substrate surface, etc. takes place. It cannot be said that the humidity control in the serial processing is sufficient.
For reducing the undesirable influence by the water before and after the HMDS processing, the method as exemplified by the prior art disclosed in Japanese Examined Patent Application Publication No. Sho 62-35264 (1987) (pp. 2–3, FIGS. 1–3), in which the serial processing from the HMDS processing to the resist application is performed in an atmosphere of nitrogen gas, is known. However, the atmosphere in which the resist application is performed has also the water content decreased, which will make it difficult to form the resist film in a uniform film thickness. Also in consideration of the amount of nitrogen gas required to completely replace the processing chamber and the time required for the replacement, etc., it will be difficult to efficiently apply the resist from the viewpoint of cost and time.
The undesirable influence by the hydrolysis of the HMDS used in the hydrophobic processing on the substrate surface due to the water is not limited to the reduced adhesion between the resist and the substrate as will be described below.
Siloxane-group substances produced by the hydrolysis of the HMDS due to the water cause reactions on the surfaces of especially amorphous silicon, etc. Resultantly, after the resist has been patterned, foreign substances are often produced on the surfaces of amorphous silicon, etc. FIG. 4 is a picture of the foreign substance. The foreign substance was observed by a scanning electronic microscope.
Such foreign substances are sufficiently able to mask the etching, and are one factor for causing defects of the pattern as etched, which has much affected yields of the products.